1. Field of the Invention
The present invention relates to a lens, and particularly relates to lenses making up a photographic lens system used for photography and the like, having reflection preventing means for preventing harmful rays.
2. Description of the Related Art
Photographic lens systems which are used for photography with a photography apparatus such as a camera for forming an image of an object are generally comprised of a plurality of lenses and the like. The front surface of each of such lenses making up the photographic lens system is generally round.
In the event that a portion of incident light rays to such a photographic lens system reflects off of the edge of the lens, i.e., the inner surface of the perimeter rim, the reflected rays may be cast into the range of the photographic aperture. In the case that such reflected light reaches the formed image, this can cause blurring or ghosting, for example, which consequently has a negative effect on the object image and deteriorates the image quality of the photographed image.
In order to suppress harmful rays which cause blurring and ghosting, known arrangement involve measures such as coating the edge plane of the lens with a black color or the like, providing a groove or the like in a direction orthogonal to the optical axis of the edge plane, and so forth, thereby suppressing generation of harmful rays.
On the other hand, the shape of the aperture for forming a photographic image is generally rectangular, with photography apparatuses such as cameras and the like. In accordance with this, various photographic lens systems using a lens formed by cutting away portions unnecessary for image formation, i.e., portions other than the effective area of the lens corresponding with the photographic screen, are proposed in Japanese Unexamined Patent Publication No. 4-177301, for example.
This arrangement aims to reduce the overall size of the lens system without narrowing the effective area of the lens to the photographic screen, by forming the front surface of the lens in a rectangular shape so as to correspond with the photographic screen (photographic aperture).
However, in the event that a part of the perimeter of the lens is cut away, as represented by the means disclosed in the above Japanese Unexamined Patent Publication No. 4-177301, the edge of the perimeter (i.e., the cut plane) of the lens is closer to the optical axis of the lens as compared to the lens before cutting.
This effect translates into an increase in the ratio of incident light rays to the lens system reflecting off of the edge of the perimeter of the lens and cast into the range of the photographic aperture so as to reach the formed image as harmful rays. This is problematic, since it has markedly adverse effects on and deteriorates the photographic image.
This will be described in further detail, with reference to FIG. 33 and FIG. 34 of the drawings attached to the present Application.
FIG. 33 is a lens configuration diagram illustrating the main cross section of a common photographic lens system comprised of multiple lenses. The optical path of a portion of the incident rays of the object light flux cast into this photographic lens system is shown.
FIG. 34 is a lens configuration diagram illustrating the main cross section of a photographic lens system wherein a portion of the perimeter of a part of the lenses in the photographic lens system shown in FIG. 33 has been cut away and re-configured. The incident rays cast into this photographic lens system, and the optical path of the harmful rays caused thereby are shown. In this FIG. 34, the portion indicated by the dotted lines (reference numeral 105) represents the portion of lens that has been cut away.
In a normal photographic lens system, light flux from the object or the like cast into the photographic lens system 101 as shown in FIG. 33, upon passing through the shutter/diaphragm mechanism 104 and the like without obstruction, follows a path such as shown by reference numeral 102 to reach a point X 101 on the same plane as the photographic aperture 103.
The point X 101 shown here is a position out of the range of the photographic aperture 103. Accordingly, in the event that incident rays are cast into the photographic lens system 101 such as that shown by reference numeral 102, there is no effect on the image including the object image (photographic results) obtained upon being imaged behind the photographic aperture 103.
Next, let us consider the case of the means disclosed in Japanese Unexamined Patent Publication No. 4-177301 and so forth, i.e., a configuration wherein a portion (shown by reference numeral 105 in FIG. 34) of the perimeter of a part of the lenses in the photographic lens system shown in FIG. 33 has been cut away.
In this case, the light flux from the object or the like cast into the photographic lens system 101A as shown in FIG. 34, upon passing through the shutter/diaphragm mechanism 104 and the like without obstruction, reflects off the edge plane 101Ab of the perimeter of the lens 101Aa at which part of the perimeter has been cut off, i.e., reflects off of the cut plane, and follows a path such as shown by reference numeral 102A to reach a point X 102 which is in the range of the photographic aperture 103.
The point X 102 shown here is a position in the range of the photographic aperture 103. Accordingly, the incident rays 102A become harmful rays which have adverse effects on the image including the object image obtained upon being imaged by the photographic lens system
In this way, in the event that a part of the perimeter of the lens is cut away, the edge (i.e., the cut plane) of the lens is closer to the optical axis of the lens, so more harmful rays (reflected rays, etc.) are propagated. Accordingly, using such a photographic lens system for photography deteriorates the photographic image obtained as a result of the photography.
However, the above Japanese Unexamined Patent Publication No. 4-177301 discloses no means for suppressing such harmful rays. Accordingly, the means as disclosed caused problem of deterioration of the photographic image due to the above-described harmful rays.